Chapter II: Significance of the Second Polar Body 352

Refutation of Minot’s theory 353

The second division of the nuclear spindle 355
involves a reduction of the ancestral germ-plasms

The theoretical necessity for such reduction 356

Phyletic origin of the germ-plasms in existing 357
species

The necessary reduction takes place by a special 358
form of nuclear division

The division which causes this reduction has 360
probably been already observed

Van Beneden’s and Carnoy’s observations 360

Two different physiological effects of 364
karyokinesis

Significance of direct nuclear division 365

Arguments in support of the view that the division 367
of the egg-nucleus which causes reduction must
occur at the end of ovogenetic development

Such nuclear division is to be found in the 368
formation of the second polar body

History of the origin of this view 368

III. THE FOREGOING CONSIDERATIONS APPLIED TO THE MALE 370
GERM-CELLS

The male germ-cells also require division in order 370
to reduce the ancestral germ-plasms

The germ-plasms of the parents must be contained 370
in the germ-plasm of the offspring

Advantages which the egg gains by the late 371
occurrence of the ‘reducing division’

The causes of unequal division in the formation of 373
polar bodies

These causes do not apply to the sperm-cell 373

Different kinds of nuclear division occur in 375
spermatogenesis

Some of these may be interpreted as ‘reducing 375
divisions’

The paranucleus (‘Nebenkern’) of spermatogenesis 376
probably contains the histogenetic nucleoplasm

IV. THE FOREGOING CONSIDERATIONS APPLIED TO PLANTS 377

V. CONCLUSIONS AS REGARDS HEREDITY 378

The germ-cell of an individual contains an unequal 378
combination of hereditary tendencies

Dissimilarity between the offspring of the same 379
parents

Identity of twins produced from a single egg 380